In the field of vehicle construction, the development and implementation of lightweight materials is becoming more and more important in order to satisfy criteria for lightweight construction. The growing concern for occupant safety also leads to the adoption of materials which improve the integrity of the vehicle during a crash while also improving the energy absorption.
A process known as Hot Forming Die Quenching (HFDQ) (also known as hot stamping or press hardening) uses boron steel sheets to create stamped components with Ultra High Strength Steel (UHSS) properties, with tensile strengths up to 1,500 MPa. The increase in strength as compared to other material allows for a thinner gauge material to be used, which results in weight savings over conventionally cold stamped mild steel components.
Typical vehicle components that can be manufactured using the HFDQ process include: door beams, bumper beams, cross/side members, A/B pillar reinforcements, and waist rail reinforcements.
In order to improve the ductility and energy absorption in key areas it is known to introduce softer zones within the same component. This improves ductility locally while maintaining the required high strength overall. By locally tailoring the microstructure and mechanical properties of certain structural components such that they comprise regions with very high strength (very hard) and regions with increased ductility (softer), it may be possible to improve their overall energy absorption and maintain their structural integrity during a crash situation and also reduce their overall weight. Such soft zones may also advantageously change the kinematic behavior in case of collapse of a component under an impact.
The soft zones can be manufactured taking into account the kinematics of the impact and the form of the component. Due to this fact, the shapes of the soft zones are becoming more and more complex.
A known solution may be the document WO2012156084, it discloses forming locally defined soft areas of the sheet metal component by means of locally tempering predetermined sub-areas of the sheet metal component by means of a laser beam method, according to which the predetermined sub-areas are exposed to a laser beam.
A drawback of this solution may be that in some particular complex forms e.g. a corner or a step may be difficult to apply a laser beam without downtimes related to the need of changing parts of the laser. Furthermore, several consecutive exposures of the component to the laser beam may be required, thus the time for defining the soft area may be increased.
EP2561946 is related to a method for the manufacture of a part of a structural component of a vehicle, intended to be connected by spot welding to a second part, starting from a coated steel plate and of a thickness of 1-3 mm, which comprises subjecting the plate to hot stamping, subsequently subjecting at least one localized and previously selected zone of the first part to a heat treatment, irradiating it with a diode laser beam of a power comprised between 500 W and 6 kW until reaching a temperature comprised between 400-900 DEG C., then leaving it to cool to change its microstructure, providing said zone with an intentionally lower martensite content and accordingly with a lower strength and greater elongation in comparison with those of its adjacent zones that have not been heat treated.
Baumann Markus et al, “Local Heat Treatment of high strength steel with zoom-optics and 10 kW-diode laser”, vol. 8239, no. 1, 2012, pages 1-9 describes a fiber-coupled 10 kW laser-source based on diode laser technology and a homogenizing zoom optical system creating rectangular sports of variable dimensions with homogeneous power density.
It is an object of the present disclosure to provide improved methods of manufacturing hot-stamped components.